The present invention relates to a method of reproducing video information recorded on an information recording disk. The inventive method includes a method of compensating for conditions in the disk and the disk player, as will be explained below.
Digital audio disks as small as 12 cm in diameter (called compact disks) are known, and have been used for recording digital audio information. Recently, disks, known as composite disks, which are the same size as a compact disk, have been developed, which contain both a frequency-modulated video signal and a pulse code modulation (PCM) signal which are superposed. An example of such a disk is shown in FIG. 3.
In FIG. 3, a first region 1a in an inner portion of the composite disk is referred to as a CD region. PCM audio information is recorded in this internal portion 1a. In an outer portion 1b referred to as a video region, a frequency-modulated video signal and PCM audio signal are superposed for purposes of recording in that region.
The frequency spectrum of the signal recorded in the video region 1b is shown in FIG. 4. The video signal includes an element having a frequency higher than that of the PCM signal. In FIG. 4, region A corresponds to the PCM signal, and region B corresponds to the video FM signal.
Recording of video signals has been carried out with the disk rotating at a speed higher than that employed in recording audio signals in the CD region 1a. Thus, reproduction of the recorded signal in the video region must be carried out at a faster rotational speed than is used for reproduction of signals in the CD region 1a. As shown in FIG. 5, for example, disk rotation might be several hundred rpm in the CD region 1a, but between 1000 and 3000 revolution per minute (rpm) in the video region 1b. For example, the rotational speed might be 2000 and several hundred rpm at the innermost track in the region 1b, and 1000 and several hundred rpm at the outermost track in the region 1b.
The difference in rotational speed necessary between the CD region 1a and the video region 1b is of particular significance when a search operation is to be carried out which crosses over the boundary between the CD region and the video region during a reproducing operation on the composite disk. In order to achieve stable change in rotational speed, some length of time (settling time) is required. As a result, a search operation crossing over the two different regions can take longer than a search which would be carried out only in one of the two regions.
One undesirable effect of this need for a longer search is deterioration in visual recognition of signals recorded in the video region because of noise arising from the length of time required for the search, and the consequent inability to input video information to a television monitor for a relatively longer period of time.
In addition to noise generated because of a relatively long search which is carried out across the CD and video regions in a composite disk, another source of noise, or otherwise poor reproduction in a video disk, might be a failure of the disk player itself, such as an unexpected power failure during reproduction of signals recorded in the video region. It is possible that reproduction might be suspended for some other reason as well. In such an event, it is necessary to restart reproduction by turning the power switch of the device on. Again, because of the relatively rapid rotation of the disk necessary for reproduction of the video signal, a longer rise time is required until the number of rotations is stabilized. During this rise time, video information is not input to the television monitor for a relatively long time, thereby possibly causing noise to be generated on the television screen, again causing deterioration of visual recognition.